Even though an early detection of cancer tissues through image scanning is very desirable to greatly improve the curing rates and also the general technologies for image scanning have made significant advancements, there are still technical difficulties and limitations faced by application of ultrasonic imaging for real time three dimensional (3D) breast scanning. Specifically, the accuracy of measurements is still not reliable due to several factors as will be further discussed below.
The mammogram scan is a preferred technique for screening of breast cancer according to the United State governmental health policy. This is mainly because of a relatively low cost and high efficiency to perform the mammogram scans. However, the accuracy of mammogram results is still questionable for women with dense breasts. Conventionally, ultrasound imaging can be used for the breast cancer screening application. U.S. Pat. No. 6,117,080, “Ultrasonic imaging apparatus and method for breast cancer diagnosis with the use of volume rendering”, (the '080 patent) describes one conventional system and method for ultrasound imaging for breast cancer screening. However, conventional ultrasound imaging is merely suitable as a complementary solution for breast cancer screening. This limitation is due to the fact that the result of ultrasound imaging is strongly dependent on the skill of the person conducting the scanning. Therefore, the data and the diagnostic results are not consistently reliable.
In a conventional ultrasound imaging for breast cancer screening, as described in the '080 patent, the breast is scanned by sliding the scanhead over the surface of the breast. The scanhead needs to be held in a constant vertical orientation so that the images are acquired from substantially parallel scan planes. Due to the variation in breast tissue thickness across the breast, the scanhead will generally move in a slight arc in the y direction as that shown in FIG. 1A according to the '080 patent's coordinate system, as the scanhead moves across the breast surface. Further, when the clinician is performing the scanning, the process maintains a constant acoustic contact with the breast and that asserts a certain amount of pressure as the scanhead moves. The constant pressure thus slightly compresses the breast tissue beneath the scanhead that leads to degradation of the accuracy and quality of data obtained from the ultrasonic image scans. The '080 patent suggested a scanning of the breast by freehand in which the user has to move the scanhead at a constant rate so that the image planes are separated in the z dimension by a substantially uniform separation which requires a few trials with slow scanhead movement and more rapid scanhead movement so the user can arrive at a scanning speed which will produce the best images. This level of skill requires significant training and practice thus limit the usefulness and acceptance of data obtained from the full breast scanning due to concerns of variations of the scanning process that may heavily depend on the skill level of an image scan operator.
The '080 patent further suggested that the arc in the y direction mentioned above can be minimized with the breast flattened out somewhat when the patient is reclining and with a water bag in between the scanhead and the breast tissue which conforms to the contours of the breast and provides good acoustic coupling between a scanning surface and the breast. This method is time consuming and does not give a consistent result and is limiting in other ways. For example, the water bag is suitable only for scanning in a down direction. Therefore, any scanning that is desired in other directions for tomography would need to take place without the water bag. However, because the water bag compresses the breast, the scans that are performed with and without the water bag would not match well.
As shown in FIG. 1B, the '080 patent also suggested an external devices attached to the scanhead to assist in determining scanhead position during a scan. A linear movement-sensing device is mounted on the scanning surface of the scanning aid and the linear sensor in the housing provides signals indicative of the position of the scanhead by means of a cable, which connects to the ultrasound system through a connector. This method again does not addressing the problem of unreliable data obtained in a scan process that requires the scan head to have multi-dimensional movement during the scan.
For these reasons, a need still exists for those of ordinary skill in the art to provide an improved method and system for medical imaging. Specifically, it is desirable that the scanning system and methods are carried out without asserting pressure onto the scanning object such that more accurate scan measurements can be obtained. It is further desirable that the scan process is automated and standardized for 3D volume data acquisition such that human operations and potential errors and variations can be minimized.